1. Gas Field Development Class Example
Use the spreadsheet Production-Forecasting.xls to look at sensitivities to reservoir parameters and tubing size.
The spreadsheet contains data for a gas reservoir with IGIP = 8 Tscf (2.3 x 1011 m3).
The model assumes that additional wells are drilled to maintain the plateau production rate. Assume a maximum of 50 wells.
The development plan aims for a plateau period of 5 years, with 60% recovery at the end of plateau.

2. Gas Field Development Class Example
Sensitivities to study (values in red give base case)
Permeability
100 md
10 md
1 md
Tubing size
7 inches
5 ½ inches
3 ½ inches
Skin
+5 (damage)
-5 (hydraulic fracture)
Aquifer size
Aquifer volume ratio = 5
Aquifer volume ratio = 10
Aquifer volume ratio = 0 (no aquifer)

3. Gas Field Development Class Example
Sensitivities to study
Number of wells.*
Length of plateau.
Field life.
Pressure drop in reservoir and tubing at start of production & end plateau.
* For some cases (e.g. low permeability), it will not be possible to maintain the required plateau rate for 5 years. In these cases, find the maximum plateau rate that can be maintained for 5 years with a maximum of 50 wells.

4. Results for 100 md reservoir
Number of wells required
Base case 25
7 in tubing 15
3.5 in tubing 50
Skin = +5 28
Skin = -5 23
No aquifer 32
Aquifer vol = 10 21
Most of the pressure drop (84 – 97% is in the tubing.
Tubing diameter is the most important parameter.
Aquifer size and skin have a smaller impact.

5. Results for 10 md reservoir
Plateau rate with 50 wells (1E6 Sm3/d)
Base case 65
7 in tubing 67
3.5 in tubing 52
Skin = +5 54
Skin = (with 38 wells)
No aquifer 58
Aquifer vol = 10 72
Comparable pressure drops in reservoir and tubing.
Skin is the most important parameter, but aquifer size and tubing are also significant.

6. Results for 1 md reservoir
Plateau rate with 50 wells (1E6 Sm3/d)
Base case 18
7 in tubing 18
3.5 in tubing 18
Skin = +5 12
Skin = -5 35
No aquifer 16
Aquifer vol = 10 18
94% of the pressure drop is in the reservoir.
Skin has a major impact on performance. Aquifer and tubing size have very little effect.